The Gram-positive bacterium Streptococcus agalactiae (or “group B streptococcus”, abbreviated to “GBS”) causes serious disease, bacteremia and meningitis, in immunocompromised individuals and in neonates. There are two types of neonatal infection. The first (early onset, usually within 5 days of birth) is manifested by bacteremia and pneumonia. It is contracted vertically as a baby passes through the birth canal. GBS colonises the vagina of about 25% of young women, and approximately 1% of infants born via a vaginal birth to colonised mothers will become infected. Mortality is between 50-70%. The second is a meningitis that occurs 10 to 60 days after birth. If pregnant women are vaccinated with type III capsule so that the infants are passively immunised, the incidence of the late onset meningitis is reduced but is not entirely eliminated.
The “B” in “GBS” refers to the Lancefield classification, which is based on the antigenicity of a carbohydrate which is soluble in dilute acid and called the C carbohydrate. Lancefield identified 13 types of C carbohydrate, designated A to O, that could be serologically differentiated. The organisms that most commonly infect humans are found in groups A, B, D, and G. Within group B, strains can be divided into 10 serotypes (Ia, Ib, II, III, IV, V, VI, VII, VIII and XI) based on the structure of their polysaccharidecapsule.
Investigations have been conducted into the development of protein-based and polysaccharide-based vaccines against GBS but currently, no GBS vaccine is commercially available. There therefore remains a need for effective vaccines against S.agalactiae infection.
It is an object of the invention to provide proteins and immunogenic compositions which can be used in the development of such vaccines.